Field of the Invention
The present invention relates to image processing to reduce an influence of scattered light due to fine particles.
Description of the Related Art
In the field of a monitoring camera or the like, a reduction in image quality of a captured image due to fine particles (e.g., trash, dust, fog) present between a camera and a subject has become problematic. The reduction in image quality is caused by light being scattered by fine particles while passing through the air and as a result of this, the contrast of a photographed image being reduced. The degree of scattering of the light scattering varies depending on the distance to the subject. Because of this, in the case where a scene in which different distances to the subjects exist mixedly is photographed, there is a possibility that an image in which the degree of reduction in contrast differs from image area to image area is acquired. As a general contrast correction technique for the image such as this the contrast of which has been reduced, there is a technique to correct the image by calculating a histogram from the photographed image and correcting the image based on the histogram (see the Japanese Patent No. 3614692). However, with the method described in the Japanese Patent No. 3614692, it is not possible to sufficiently correct an image in which the degree of reduction in contrast differs from area to area. Consequently, as a technique to correct the reduction in contrast for each area, there is a technique that uses a dark channel prior (see the U.S. Pat. No. 8,340,461). In this technique, from the RGB minimum values (dark channel) in a local area of a photographed image, the degree of scattering of light due to fine particles is estimated and the contrast correction is performed for each local area.
However, in the case where the contrast correction for each local area is performed by using the method described in the U.S. Pat. No. 8,340,461, it is not possible to guarantee the brightness of the entire image, and therefore, there is a possibility that the brightness of the entire image becomes brighter or darker compared to appropriate brightness.